1,294 research outputs found
A micromechanics-enhanced finite element formulation for modelling heterogeneous materials
In the analysis of composite materials with heterogeneous microstructures,
full resolution of the heterogeneities using classical numerical approaches can
be computationally prohibitive. This paper presents a micromechanics-enhanced
finite element formulation that accurately captures the mechanical behaviour of
heterogeneous materials in a computationally efficient manner. The strategy
exploits analytical solutions derived by Eshelby for ellipsoidal inclusions in
order to determine the mechanical perturbation fields as a result of the
underlying heterogeneities. Approximation functions for these perturbation
fields are then incorporated into a finite element formulation to augment those
of the macroscopic fields. A significant feature of this approach is that the
finite element mesh does not explicitly resolve the heterogeneities and that no
additional degrees of freedom are introduced. In this paper, hybrid-Trefftz
stress finite elements are utilised and performance of the proposed formulation
is demonstrated with numerical examples. The method is restricted here to
elastic particulate composites with ellipsoidal inclusions but it has been
designed to be extensible to a wider class of materials comprising arbitrary
shaped inclusions.Comment: 28 pages, 12 figures, 2 table
Charge order in Magnetite. An LDA+ study
The electronic structure of the monoclinic structure of FeO is
studied using both the local density approximation (LDA) and the LDA+. The
LDA gives only a small charge disproportionation, thus excluding that the
structural distortion should be sufficient to give a charge order. The LDA+
results in a charge disproportion along the c-axis in good agreement with the
experiment. We also show how the effective can be calculated within the
augmented plane wave methods
Influence of soil tillage on oats yield in Central Bohemia Region
ArticleThe paper describes results of the field experiment with two technologies of oats crop
stand establishment. First technology is conventional technology and second is no
-
tillage
technology. The arti
cle describes an experiment which was conducted in years 2013
–
2017. The
experiments were located in Nesperská Lhota at Central Bohemia region. Altitude of selected
field is 460 m. The experimental field is covered by a light cambi
-
soil. The differences bet
ween
the two
technologies stand establishment are discussed. Statistical evaluation was performed on
both methods in the parameter number of tillers per m
2
and yield. Crop yield is the basic
indicator of agricultural production and usually affected by qual
ity of soil tillage. One of the
parameters affecting the yield is tillage (technology, working tools, depth, turning of soil etc.).
Tillage depends mainly on the depth of processing and other quality parameters. An
examination of the crop yield is necessar
y in terms of sensitivity, depending on agro
-
technical
conditions. Among those can be included processing plant soil nutrition and plant protection.
It's always necessary commemorate, in these experiments can't be excluded some parameters
like locality or
meteorological parameter influences. Field trial was conceived as multi
-
year
experiment with minimal changes of agro
-
technical conditions. During the experiment, the
positive effect of conventional technology on crop yields was found. This difference was
r
eflected in the number of tillers and in total yield. The measurement shows the beneficial effect
of the loosening of soil on the state of the oat crops. The results of experiment show that, the
average yield in 5 years observation was 2.11
t
ha
-
1
for no
-
t
ill technology and 4.22
t
ha
-
1
for
conv
entional technology of tillage
Comparison of tillage systems in terms of water infiltration into the soil during the autumn season
ArticleThe soil belongs to the most valuable parts of the planet Earth. It is, endangered by
water erosion, which causes huge destruction every year, or damage to farmland. More than half
of the agricultural land in the Czech Republic is threatened by water erosion. The measurement
was performed in the location Nesperská Lhota. The trial has been established on loamy sand
Cambisol. In the field experiment, there were created 6 different variants which wad differed by
soil tillage and crop. In the individual variants maize and oats were located. The field trial has
been existing for a long time, as it was founded in 2009. Two measuring methods of water
infiltration were used for the measurements: a mini disk infiltrometer and a single ring. The
measurement was performed in the period of September 2016 before the harvest of maize. The
soil aggregates were already stabilized at that time after all tillage operations. The measurement
result showed the difference between the methods of soil tillage. The greatest ability of infiltration
had a variant of maize with inter-row oats. Surprisingly, it was followed by maize, which was
processed by ploughing technology. The lowest infiltration capacity was showed by oats reduced
by soil tillage. A variant without vegetation had the second lowest infiltration. Our results
obtained at rate of water infiltration into the soil affirm the need to control measures in the late
vegetative stages. It is important for most of the rainfall to be quickly infiltrated so that it prevents
the formation of massive surface runoff
Changes in soil properties and possibilities of reducing environmental risks due to the application of biological activators in conditions of very heavy soils
This study aims at verifying the effect of farmyard manure (FYM) and of selected
activators (Z'fix and NeoSol) on changes of soil properties. Their application should lead to
improvement of soil physical properties and of organic matter fixation, to reduction of
environmental risks, e.g. of tillage energy requirements. Experimental variants (0.7 ha each) were
as follows: I (FYM with Z'fix); II (FYM with Z'fix + NeoSol); III (FYM); IV (Control NPK only).
FYM was applied at rates: 50 t ha-1
(2014); 30 t ha-1
(2016). Additional NPK fertilizer (I–IV) was
applied according to annual crop nutrient normative. The agent Z'fix was used as an activator of
FYM biological transformation (5.5 kg t
-1
). The agent NeoSol was used as soil activator
(200 kg ha-1
; annually). In order to verify the effect, cone index, bulk density, tillage implement
draft and chemical soil components (Humus, C/N ration and Ntot) were measured annually.
Compared to the control, the application of FYM combined with the mentioned agents (I–III)
increased Ntot more than two times. Moreover, it decreased (I–III) bulk density by 8.7%. Tillage
implement draft decreased by 3% after the application of FYM with Z’fix (I, II). The study
confirmed that FYM application combined with utilization of activators positively influenced soil
fertility and helped to reduce environmental risks
Effect of PTO-driven tillage machines on soil particles transfer
ArticleDisplacement of soil particles by erosion can be seen as a major threat to the quali
ty
of agricultural land in the conditions of Czech Republic. While the effects of water and wind
erosion have long been investigated and reported, the effect of soil tillage technology on soil
particles translocation are relatively new area of agriculture
research. Soil tillage may contribute
to the undesirable translocation of soil particles towards lower
-
lying parts of fields especially on
slopes. The effect of soil tillage implements on soil particle translocation has not been sufficiently
explained yet.
The object of this research was to assess the influence of PTO (power takeoff)
-
driven tillage machines on soil particle translocation during secondary tillage (soil preparation).
Measurements to determine the displacement of soil particles were performed
in location
Nesperská Lhota in the Central Bohemia Region. Measurements were performed on a sandy loam
cambisol after harvest winter cereals (winter wheat). To indicate displacement of soil particles
was used grit of white limestone (size 10
–
16
mm). Limest
one was put down into the trench with
known position orthogonal to the direction of working operations. Subsequently were performed
working operations in the specified sequence. Limestone particles were counted and weighed in
each section. It was detected
by measuring the different nature of displacement for each machine.
Statistical significance of differences in the weight of translocated particles was evaluated for
different type of machines
Plantograf V18 – new construction and properties
ArticleThe article describes Plantograf
V18, a planar tactile transducer, which converts the
applied pressure into electric signal and enables a graphical presentation of the measured data;
the new version V18 comes with some significant improvements and modifications. The device
may be used ev
erywhere where the pressure distribution between an object and surface is to be
determined, e.g. in medicine or automotive industry. The article contains the detailed description
of the transducer design and its electronic control circuits, as well as the
yet unpublished
measurements of pressure sensitivity with 3.5
mm electrodes
Surface water runoff of different tillage technologies for maize
ArticleThe present paper is focused on the evaluation of efficiency of soil-conservation
technologies to reduce surface water runoff in Central Bohemia Region. In the last years, there
has been an increase in maize planting on hillslope plots due to the construction of many biogas
plants in conditions of Czech Republic. It enhances the risk of water erosion because the
occurrence of sloping lands in the Czech Republic is high. To evaluate the technologies of stand
establishment a field trial was laid out with four treatments of maize planting. The trial was laid
out on a plot with light soil and slope of around 12%. It was a multi-year trial. To measure erosion
parameters a rainfall simulator was used (measurement of surface runoff). The values obtained
in two seasons show a positive effect of the soil surface cover by organic matter when reduced
soil tillage was used. Soil loss also decreased at the same time compared to treatments with
conventional soil tillage. It was found up to six-fold reduction in surface runoff by appropriate
soil tillage technology during two seasons of measurement
Fast optical control of spin in semiconductor interfacial structures
We report on a picosecond-fast optical removal of spin polarization from a
self-confined photo-carrier system at an undoped GaAs/AlGaAs interface
possessing superior long-range and high-speed spin transport properties. We
employed a modified resonant spin amplification technique with unequal
intensities of subsequent pump pulses to experimentally distinguish the
evolution of spin populations originating from different excitation laser
pulses. We demonstrate that the density of spins, which is injected into the
system by means of the optical orientation, can be controlled by reducing the
electrostatic confinement of the system using an additional generation of
photocarriers. It is also shown that the disturbed confinement recovers within
hundreds of picoseconds after which spins can be again photo-injected into the
system
- …